One morally important distinction here is between conscripted and voluntary military service. As you are probably aware, the United States currently has an all-voluntary military; every soldier is a soldier by choice. This has not always been the case (either in the U.S. or elsewhere). Nations sometimes requires military service of all citizens as a matter of course and/or utilize a draft during wartime.
Let's focus first on those whose service is voluntary. Our attitudes toward those who volunteer for military service are, in my estimation, incoherent. We have become too quick to "thank them for their service" without due concern for the morality of their service. Classical just war theory divides the moral appraisal of war into two: there is the question of whether a nation's waging war in a given set of circumstances is just, and there's the question of whether a war is justly waged (whether, for example, the tactics or strategies used to pursue victory are just). Soldiers can therefore err morally...

Kantian ethics does appeal to notions of consistency, but the consistency that Kantian morality requires is not consistency in respecting "preferences" (as you expressed it.) Rather, Kantian morality requires consistency in respect for practically rational agency, i.e, the capacity to set one's ends and choose the means to one's ends. Kant believed (not incorrectly, for the most part) that non-human animals lack this capacity and hence are not owed respect in this sense. Indeed, Kant held that, strictly speaking, we have no moral obligations to animals at all; animals lack the property (practical rational agency) that lends something moral standing.
Many moral philosophers, including many Kantians, find Kant's conclusions troubling, inasmuch as it certainly seems intuitively plausible that we can wrong animals. Kantians have tried a number of solutions to rescue Kantian ethics from this position. Here are some articles in that vein:
https://philpapers.org/rec/CHOADK
https://philpapers.org/rec/DENKCO-2...

I'm not sure that most contemporary Kantian moral philosophers agree with Kant on the morality of prostitution. As you note, prostitution does not seem to make use of one's own humanity in a way that's fundamentally different from other forms of work or labor which are clearly morally permissible. Why think that prostitution, unlike farming, involves the wrongful use of ourselves merely as a means?
Much of the reason is that Kant was deeply skeptical about the compatibility of sexual desire with the moral requirement to treat rational agents as ends in themselves rather than merely as a means. He writes: “Sexual union is the reciprocal use that one human beings makes of the sexual organs and capacities of another” for the purpose of enjoyment. As Kant saw it, sexual desire is not a desire for a person's good but for the use of their body for one's own physical pleasure. Hence, sexual desire is fundamentally at odds with respect for others' rational natures. Sex is animalistic in that we treat ourselves ...

Unfortunately, this is a tricky question for Kantian ethics to address.
On its face, it might appear that procreation (bringing a child into existence) in order to advance one’s own happiness treats the child merely as a means: One ‘uses’ the child to promote one’s own happiness.
But things get more complicated once we attend to exactly what this Kantian imperative says. The Kantian moral requirement you mention states that we are not to treat “humanity” merely as a means. There are debates as to exactly what Kant had in mind by “humanity” but the standard view is that “humanity” means the capacity for rational agency — the ability to choose our ‘ends’ (our goals or objectives) and the best means to those ends. But a newborn lacks “humanity” in this sense; it cannot choose ends for itself, etc. Nor can a fetus. All the more, a child who does not yet exist does not have humanity! Hence, it would appear that the apparent answer to your question is ‘no’: You cannot treat someone’s capacity for...

Setting aside the question of whether the principle 'better to let many guilty go free than to wrongly imprison a single innocent person' is the rationale for the presumption of innocence, that utilitarians would reject the principle is not as clearcut as you appear to assume. We seem to be considering two possibilities:
(a) letting some number of guilty persons (you say 'many') go free but thereby ensuring that an innocent person is not punished
(b) punishing an innocent person but ensuring that 'many' guilty persons are also punished
For utilitarians, the question of whether (a) or (b) is morally preferable will turn on empirical facts or tendencies. You suggest that utilitarians will opt for punishing the guilty even at the cost of punishing the innocent "if the guilty parties are liable to do harm enough to outweigh the suffering of the wrongly imprisoned innocent party." I suspect this move overlooks two factors that might tilt the balance of costs and benefits (happiness and unhappiness) in...

What makes this issue tricky is that the question seems to equivocate on the notions of "right" and "just."
Suppose (as seems likely) that rebelling against a democratic government involves conduct that the government in question has declared illegal. It seems clear that such rebellious conduct can't be "right" or "just" in the sense of of being legally permissible . It would, after all, threaten incoherence if a code of law has an 'out clause' permitting rebellion, akin to "here are the laws, but you can rebel against them without penalty." That would render that system of law toothless with respect to its authority.
So if there is right to rebel, the right can't be a legal or political one. It would have to be a moral or "natural" right. Indeed, this seems to be what political theorists such as Locke (and the framers of the U.S. Constitution he inspired) had in mind when they referenced a right to rebel against unjust governments. I won't take on the big project of defending the existence of such...

Standardly, philosophers think of pride as closely related to deservedness. Pride, on this view, amounts to taking pleasure in one's excellence or accomplishments. To have proper pride therefore requires that one have an accurate appraisal of one's excellence or accomplishments. To take more pleasure than one's excellence or accomplishments merit is to exhibit vanity. To take less pleasure than one's excellence or accomplishments merit is to exhibit excessive modesty or a lack of self-respect. (This analysis of pride owes much to Aristotle's discussion of pride in the Nicomachean Ethics .)
So what of those who (as you ask) are 'proud of' their nation's past accomplishments, or in the victories of their favorites sports teams, etc.? On its face, pride seems unjustified in these cases. For these are not the person's accomplishments but the accomplishments of others. It would, I agree, be a form of noxious self-flattery for someone born well after the Second World War to take literal pride in the US'...

Nice question! Here's a quick reconstruction of your reasoning:
(1) In order to know what X is, you need to observe instances of X.
(2) But one could only know one is observing instances of X if one already knew what X is.
(3) Hence, one can neither know what X is nor know whether one is observing instances of X.
(3) looks like a pretty powerful skeptical conclusion: It would seem like we can't know whether a certain thing is beautiful unless we know what beauty is, but we can't know what beauty is unless we know which things are beautiful. We certainly seem stuck -- and the same reasoning could be used to generate skeptical conclusions about other important philosophical concepts (such as goodness, virtue, and so on).
Is there a way out of this conundrum? There are a lot of complex issues here, so let me just mention some possible ways out and leave it to you to assess their plausibility:
Testimony Others might be in a credible position to tell us which things are beautiful or what beauty is....

Based on your description of the scenarios you're envisioning, I'm not seeing any inherent moral difference between the scientist and those who procreate children in the 'ordinary' or 'natural' way. Whatever moral reasons seem to weigh either for or against procreating children knowing that there is a high probability they will have "short and extremely bad lives" apply equally to the scientist as to anyone else who procreates under the same conditions. Perhaps you're seeking to highlight that the scientist 'grows' humans outside of a "natural context" as a morally significant factor that makes his procreative acts morally worse. There I'd have to say that while his creating the offspring in some sort of artificial or 'unnatural' way adds to the 'ick' factor, but it's hard to see how there's any moral difference there.
No doubt many people attach some moral significance to 'naturalness' when it comes to procreation. They might argue that somehow natural procreation isn't subject to the same moral...

Thanks for your question.
Before my response, a brief observation: You speak of principles being "maximized". I suspect you're confusing Kant's notion of a maxim with some other idea from moral philosophy (perhaps the utilitarian claim that right actions are those that maximize well-being). A maxim, for Kant, is a justifying principle of action with the form "I will do act A in circumstances C to achieve end E". Kant's Formula of Universal Law requires that we act only on maxims that can be consistently universalized. There's a lot of controversy as to precisely what it means for a maxim to be consistently universalizable. Here's a description, provided by Robert Johnson in his Stanford Encyclopedia of Philosophy article on Kant's moral philosophy, of the procedure to be used to evaluate whether a maxim can be consistently universalized:
First, formulate a maxim that enshrines your reason for acting as you propose. Second, recast that maxim as a universal law of nature governing all rational agents,...